PRESS
Biomimetic Ratchets
Insects
provide examples
of many cunning
stratagems
to cope with
the challenges
of living
in a world
dominated
by surface
forces. Despite
being the
current masters
of the land
environment,
they are
at constant
risk of being
entrapped
in liquids,
which they
prevent by
having waxy
and hairy
surfaces.
The problem
is particularly
acute in
an enclosed
space, such
as a plant
gall. Using
secreted
wax to efficiently
parcel and
transport
their own
excrement,
aphids were
able to solve
this problem
200 Myr ago.
Here, we
report on
the physical
and physiological
significance
of this ingenious
solution.
The secreted
powdery wax
has three
distinct
roles: (i)
it is hydrophobic,
(ii) it creates
a microscopically
rough inner
gall surface
made of weakly
compacted
wax needles
making the
gall ultra-hydrophobic,
and (iii)
it coats
the honeydew
droplets
converting
them into
liquid marbles,
that can
be rapidly
and efficiently
moved.
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